Polycarbonates derived from reactions involving organic dihydroxy compounds and carbonic acid derivatives have found extensive commercial application because of their excellent mechanical and physical properties. These thermoplastic polymers are particularly suited for the manufacture of molded articles where impact strength, rigidity, toughness, thermal and dimensional stability as well as excellent electrical properties are required.
However, one deficiency of polycarbonate when used in molded articles is the heat deflection temperature of the polycarbonate polymer. As determined by ASTM D-648/72, the heat deflection temperature defines the temperature at which a 0.25 mm deflection occurs when a specimen 127 mm in length, 13 mm in depth and 3 mm to 13 mm in width are subjected to a load applied at its center to give maximum fiber stresses of 66 psi (455 kPa) or 264 psi (1820 kPa). Typical polycarbonates known in the prior art exhibit heat deflection temperatures of from about 135.degree. to 141.degree. C. at a 264 psi load.
In accordance with the present invention, a copolycarbonate is provided with improved heat deflection temperature and good physical properties.
The copolycarbonate of the invention comprises the reaction product of an aromatic diphenol, an aromatic, sulfonyl diphenol, a dihydroxybiphenyl and a carbonic acid derivative such as phosgene or carbonyl bromide.
Copolycarbonates and terpolycarbonates based on aromatic sulfonyl diphenols are known in the art (see U.S. Pat. Nos. 3,023,101, 3,271,367 and 3,912,688) as are copolycarbonates based on biphenyls (U.S. Pat. No. 3,748,303). Also of interest as background information are U.S. Pat. Nos. 3,065,274 and 3,551,501.